1. Field of the Invention
The present invention relates to a fastener design, particularly to a self-drilling wall anchor device.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional self-drilling wall anchor comprises a threaded member 11, an outer sleeve 12 penetrated by the threaded member 11, and a drill element 13 connected to the threaded member 11. Wherein, the threaded member 11 is made of metal and has a shank 111, a head 112 disposed at one end of the shank 111, an engaging part 113 disposed at the other end of the shank 111, and a threaded section 114 spirally disposed on the shank 111. Herein, the threaded section 114 has a first diameter a1 larger than a second diameter a2 of the engaging part 113.
The outer sleeve 12 is made of plastic and allows the threaded member 11 to penetrate. The outer sleeve 12 has a body 121, a through hole 122 defined in the body 121, a threaded portion 123 disposed on the body 121, and arms 124 disposed on the body 121, opposite to the threaded portion 123. Wherein, the body 121 has a first end 1211 and a second end 1212 defined thereon, the first end 1211 and the second end 1212 are communicated with the through hole 122, the threaded portion 123 is disposed near the second end 1212, and a peripheral flange 1231 whose outer diameter is larger than a main diameter of the body 121 is protruded on the second end 1212. A plurality of slots 1241 are defined on the arms 124. Moreover, the through hole 122 has a first area 1221 adjacent to the first end 1211, and a second area 1222 connected to the first area 1221 and adjacent to the second end 1212. The second area 1222 has a second area diameter b2 that is larger than a first area diameter b1 of the first area 1221. Whereby, when the threaded member 11 enters the through hole 122, the first area 1221 accommodates the engaging part 113, and the second area 1222 accommodates the threaded section 114. Additionally, the second area diameter b2 is larger than the first diameter a1, and the first diameter a1 is larger than the first area diameter b1.
The drill element 13 is made of metal. The drill element 13 has a drilling member 131 and a bore 132 disposed opposite to the drilling member 131 for fixing the engaging part 113. When the threaded member 11 enters the through hole 122 of the outer sleeve 12, the threaded section 114 is accommodated in the first area 1221, and the engaging part 113 protrudes out of the first end 1211 for being fixed to the drill element 13. Thereby, the assemblage of the self-drilling wall anchor device 1 is complete.
Referring to FIGS. 2 and 3, in using, the drill element 13 is set against a gypsum object 2. Thereafter, the threaded member 11 brings the outer sleeve 12 into the gypsum object 2 by screwing. At the time the peripheral flange 1231 touches the gypsum object 2, the threaded member 11 keeps screwing and rotating, so that the arms 134 start deforming and twisting. When the arms 124 achieve their extreme deformation and twisting, the threaded member 11 stops rotating since the screwing thereof is complete, and the threaded member 11 is firmly fixed.
In practice, the second area diameter b2 of the outer sleeve 12 is larger than the first diameter a1 of the threaded section 114. Thus, an interstice is incurred between the threaded section 114 and the second area 1222. While the threaded member 11 keeps screwing and the arms 124 continue deforming and twisting, the threaded section 114 can not block the second area 1222 thoroughly, so the deformed and twisted arms 124 easily get into the interstice between the threaded section 114 and the second area 1222 and even break a part of the gypsum object 2. Subsequently, the fixed self-drilling wall anchor device 1 can only grip the rest of the gypsum object 2 that is not broken. Moreover, the twisted and deformed arms 124 are simply propped by the peripheral flange 1231. Therefore, the self-drilling wall anchor device 1 can not provide a satisfactory gripping effect since it might easily retract.